What is the primary function of a hot water cylinder?

The primary function of a hot water cylinder is to store and provide a steady supply of hot water for domestic use. This means that the cylinder is designed to heat water and maintain it at a certain temperature so that it is readily available when needed for various applications such as bathing, cleaning, or cooking.

Hot water cylinders are typically insulated to retain heat, ensuring that the hot water remains at a desirable temperature over time, even when there is not constant demand. This setup allows for the efficient use of energy, as water can be heated during off-peak times and stored for use throughout the day.

In contrast, the other options do not accurately describe the primary function of a hot water cylinder. While instant water heating systems and cooling systems have their specific uses, they do not relate to the fundamental role of a hot water cylinder in storing and supplying heated water. Similarly, regulating water pressure is an important aspect of plumbing systems but is not the role of a hot water cylinder itself.